ARS | Publication request: INTERACTIONS OF MALT AND BARLEY (HORDEUM VULGARE L.) ENDOPROTEINASES WITH THEIR ENDOGENOUS INHIBITORS

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 25, 2001
Publication Date: N/A

Interpretive Summary: In order to produce malt that will make good beer, a portion of the proteins of the barley that is malted must be degraded into amino acids and peptides. Enzymes that form during malting carry out this process, but the barley and malt both contain proteins (called inhibitors) that can stop these enzymes from acting. In order to develope malting barleys that will form malts that are optimally adapted for beer production, we need to understand exactly how the inhibitors interact with the enzymes to stop them from acting. This paper describes a method I developed for measuring the interactions of the inhibitors and enzymes and how it was used to test the effectiveness of various techniques for stopping these molecules from interacting. If a technique for destroying the inhibitor-enzyme interactions can be found, this will make it easier to measure the malting quality of newly developed barley lines. The method was used to characterize how the inhibitors and enzymes interact, but the only treatment that disrupted the interactions was to heat the samples to boiling. This boiling destroyed the enzymes, indicating that it is going to be very hard to devise ways to measure the total amount of protein- degrading enzymes that are present in malts. By altering the enzyme- inhibitor analysis method, I developed an improved biochemical method for concentrating the inhibitors. This will make it easier to study these important proteins in the future. This research will help scientists who need to study the biochemistry of malt production and knowledge obtained by applying the methods will make it easier for plant breeders to produce new barleys that have improved malting quality.

Technical Abstract: For producing worts that are optimal for beer production, some, but not all, of the barley proteins must be degraded during malting and mashing. This protein hydrolysis is controlled by endoproteinases and, in turn, is partially regulated by the presence of low molecular weight (LMW) proteinaceous inhibitors. This paper reports studies of the interactions between the proteinases and inhibitors and an 'affinity' method for concentrating the inhibitors. The malt inhibitors (I) and proteinases (E) quickly formed strong (EI) complexes when dissolved together, and all of the I was complexed. Heating at 100C, but not 70C, dissociated the complex, even though the enzyme activities were destroyed at 70C. The released I readily recomplexed with fresh E. Barley, however, contained insufficient E to complex all of its I complement. The EI complex was treated with salts, detergents and reducing agents to release active E molecules, but none disrupted the complex. By removing the LMW proteins from a malt EI extract and dissociating the complex by heating, the concentration of I molecules was greatly increased. This 'affinity' method can thus be used to concentrate the I molecules for further purification.